Acts::Result< T, E > Class Template Reference

Class which encapsulates either a valid result, or an error. More...

#include <Acts/Utilities/Result.hpp>

Inheritance diagram for Acts::Result< T, E >:

Public Types
using	ErrorType = E
	Type alias for the error type contained in failed result.
using	ValueType = T
	Type alias for the value type contained in successful result.

Public Member Functions
	Result ()=delete
	Default construction is disallowed.
	Result (const Result< T, E > &other)=delete
	Copy construction is disallowed.
	Result (Result< T, E > &&other) noexcept
	Move construction is allowed.
template<typename T2> requires (!std::same_as<T, E> && !std::constructible_from<T, E> && !std::convertible_to<T, E> && !std::constructible_from<E, T> && !std::convertible_to<E, T> && !(std::convertible_to<T2, T> && std::convertible_to<T2, E>))
	Result (T2 value) noexcept
	Constructor from arbitrary value This constructor allows construction from any value.
template<typename C> requires std::invocable<C, T&&>
auto	and_then (C &&callable) &&
	Bind a function to this result monadically.
template<typename C> requires std::invocable<C, const T&>
auto	and_then (C &&callable) const &
	Bind a function to this result monadically.
E	error () &&noexcept
	Returns the error by-value.
E &	error () &noexcept
	Returns a reference to the error stored in the result.
const E &	error () const &noexcept
	Returns a reference to the error stored in the result.
bool	ok () const noexcept
	Checks whether this result contains a valid value, and no error.
const T &	operator* () const noexcept
	Returns a reference into the variant to the valid value.
T &	operator* () noexcept
	Returns a reference into the variant to the valid value.
const T *	operator-> () const noexcept
	Allows to access members of the stored object with res->foo similar to std::optional.
T *	operator-> () noexcept
	Allows to access members of the stored object with res->foo similar to std::optional.
Result< T, E > &	operator= (const Result< T, E > &other)=delete
	Assignment is disallowed.
Result< T, E > &	operator= (Result< T, E > &&other) noexcept
	Move assignment is allowed.
template<typename T2> requires (!std::same_as<T, E> && !std::constructible_from<T, E> && !std::convertible_to<T, E> && !std::constructible_from<E, T> && !std::convertible_to<E, T> && !(std::convertible_to<T2, T> && std::convertible_to<T2, E>))
Result< T, E > &	operator= (T2 value) noexcept
	Assignment operator from arbitrary value This operator allows construction from any value.
template<typename C> requires std::invocable<C, T&&>
auto	transform (C &&callable) &&
	Transforms the value contained in this result.
template<typename C> requires std::invocable<C, const T&>
auto	transform (C &&callable) const &
	Transforms the value contained in this result.
T &	value () &
	Retrieves the valid value from the result object.
const T &	value () const &
	Retrieves the valid value from the result object.
template<typename U> requires (std::same_as<std::decay_t<U>, T>)
std::conditional_t< std::is_reference_v< U >, const T &, T >	value_or (U &&v) const &
	Retrieves the valid value from the result object, or returns a default value if no valid value exists.

Static Public Member Functions
static Result< T, E >	failure (E error)
	Static helper factory which forces assignment as an error.
static Result< T, E >	success (T value)
	Static helper factory which forces assignment as valid value.

Detailed Description

template<typename T, typename E = std::error_code>
class Acts::Result< T, E >

Class which encapsulates either a valid result, or an error.

Template Parameters

T	The valid result value
E	The error, defaults to std::error_code

Member Typedef Documentation

ErrorType

template<typename T, typename E = std::error_code>

using Acts::Result< T, E >::ErrorType = E

Type alias for the error type contained in failed result.

ValueType

template<typename T, typename E = std::error_code>

using Acts::Result< T, E >::ValueType = T

Type alias for the value type contained in successful result.

Constructor & Destructor Documentation

Result() [1/4]

template<typename T, typename E = std::error_code>

Acts::Result< T, E >::Result ( )

delete

Default construction is disallowed.

Result() [2/4]

template<typename T, typename E = std::error_code>

Acts::Result< T, E >::Result ( const Result< T, E > & other )

delete

Copy construction is disallowed.

Result() [3/4]

template<typename T, typename E = std::error_code>

Acts::Result< T, E >::Result ( Result< T, E > && other )

noexcept

Move construction is allowed.

Parameters

other

The other result instance to move from

Result() [4/4]

template<typename T, typename E = std::error_code>

template<typename T2>
requires (!std::same_as<T, E> && !std::constructible_from<T, E> && !std::convertible_to<T, E> && !std::constructible_from<E, T> && !std::convertible_to<E, T> && !(std::convertible_to<T2, T> && std::convertible_to<T2, E>))

Acts::Result< T, E >::Result ( T2 value )

noexcept

Constructor from arbitrary value This constructor allows construction from any value.

This constructor is only enabled if T and E are unambiguous, meaning they cannot be implicitly converted and there is T cannot be constructed from E and vice-versa. This means that when this is invoked, the value can be propagated to the underlying variant, and the assignment will be correct, and error will be an error, and a value will be a value.

Note

If T and E are ambiguous, use the success and failure static factory methods.

Template Parameters

T2	Type of the potential assignment

Parameters

value

The potential value, could be an actual valid value or an error.

Member Function Documentation

and_then() [1/2]

template<typename T, typename E = std::error_code>

template<typename C>
requires std::invocable<C, T&&>

auto Acts::Result< T, E >::and_then

(

C &&

callable

)

&&

Bind a function to this result monadically.

This function takes a function f and, if this result contains a valid value x, returns f(x). If the type of x is T, then f is expected to accept type T and return Result<U>. In this case, transform would return the unhelpful type Result<Result<U>>, so and_then strips away the outer layer to return Result<U>. If the value is invalid, this returns an invalid value in Result<U>.

Parameters

[in]

callable

The transformation function to apply.

Note

This is the rvalue version.

This functions is >>= on the functor in A of Result<A, E>.

Returns

The modified valid value if exists, or an error otherwise.

and_then() [2/2]

template<typename T, typename E = std::error_code>

template<typename C>
requires std::invocable<C, const T&>

auto Acts::Result< T, E >::and_then

(

C &&

callable

)

const &

Bind a function to this result monadically.

This function takes a function f and, if this result contains a valid value x, returns f(x). If the type of x is T, then f is expected to accept type T and return Result<U>. In this case, transform would return the unhelpful type Result<Result<U>>, so and_then strips away the outer layer to return Result<U>. If the value is invalid, this returns an invalid value in Result<U>.

Parameters

[in]

callable

The transformation function to apply.

Note

This is the lvalue version.

This functions is >>= on the functor in A of Result<A, E>.

Returns

The modified valid value if exists, or an error otherwise.

error() [1/3]

template<typename T, typename E = std::error_code>

E Acts::Result< T, E >::error ( ) &&

noexcept

Returns the error by-value.

Note

If res.ok() this method will abort (noexcept)

Returns

The error

error() [2/3]

template<typename T, typename E = std::error_code>

E & Acts::Result< T, E >::error ( ) &

noexcept

Returns a reference to the error stored in the result.

Note

If res.ok() this method will abort (noexcept)

Returns

Reference to the error

error() [3/3]

template<typename T, typename E = std::error_code>

const E & Acts::Result< T, E >::error ( ) const &

noexcept

Returns a reference to the error stored in the result.

Note

If res.ok() this method will abort (noexcept)

Returns

Reference to the error

failure()

template<typename T, typename E = std::error_code>

Result< T, E > Acts::Result< T, E >::failure ( E error )

static

Static helper factory which forces assignment as an error.

Parameters

error

The error to assign. Will not be converted to T.

Returns

Initialized result object

ok()

template<typename T, typename E = std::error_code>

bool Acts::Result< T, E >::ok ( ) const

noexcept

Checks whether this result contains a valid value, and no error.

Returns

bool Whether result contains an error or not.

operator*() [1/2]

template<typename T, typename E = std::error_code>

const T & Acts::Result< T, E >::operator* ( ) const

noexcept

Returns a reference into the variant to the valid value.

Note

If !res.ok(), this method will abort (noexcept)

Returns

Reference to value stored in the variant.

operator*() [2/2]

template<typename T, typename E = std::error_code>

T & Acts::Result< T, E >::operator* ( )

noexcept

Returns a reference into the variant to the valid value.

Note

If !res.ok(), this method will abort (noexcept)

Returns

Reference to value stored in the variant.

operator->() [1/2]

template<typename T, typename E = std::error_code>

const T * Acts::Result< T, E >::operator-> ( ) const

noexcept

Allows to access members of the stored object with res->foo similar to std::optional.

Note

If !res.ok(), this method will abort (noexcept)

Returns

Pointer to value stored in the variant.

operator->() [2/2]

template<typename T, typename E = std::error_code>

T * Acts::Result< T, E >::operator-> ( )

noexcept

Allows to access members of the stored object with res->foo similar to std::optional.

Note

If !res.ok(), this method will abort (noexcept)

Returns

Pointer to value stored in the variant.

operator=() [1/3]

template<typename T, typename E = std::error_code>

Result< T, E > & Acts::Result< T, E >::operator= ( const Result< T, E > & other )

delete

Assignment is disallowed.

operator=() [2/3]

template<typename T, typename E = std::error_code>

Result< T, E > & Acts::Result< T, E >::operator= ( Result< T, E > && other )

noexcept

Move assignment is allowed.

Parameters

other

The other result instance, rvalue reference

Returns

The assigned instance

operator=() [3/3]

template<typename T, typename E = std::error_code>

template<typename T2>
requires (!std::same_as<T, E> && !std::constructible_from<T, E> && !std::convertible_to<T, E> && !std::constructible_from<E, T> && !std::convertible_to<E, T> && !(std::convertible_to<T2, T> && std::convertible_to<T2, E>))

Result< T, E > & Acts::Result< T, E >::operator= ( T2 value )

noexcept

Assignment operator from arbitrary value This operator allows construction from any value.

The same rules as for the Result(T2 value) constructor apply.

• Template Parameters

  T2	Type of the potential assignment

  Parameters

  value

  The potential value, could be an actual valid value or an error.

  Returns

  The assigned instance

success()

template<typename T, typename E = std::error_code>

Result< T, E > Acts::Result< T, E >::success ( T value )

static

Static helper factory which forces assignment as valid value.

Parameters

value

The valid value to assign. Will not be converted to E.

Returns

Initialized result object

transform() [1/2]

template<typename T, typename E = std::error_code>

template<typename C>
requires std::invocable<C, T&&>

auto Acts::Result< T, E >::transform

(

C &&

callable

)

&&

Transforms the value contained in this result.

Applying a function f to a valid value x returns f(x), while applying f to an invalid value returns another invalid value.

Parameters

[in]

callable

The transformation function to apply.

Note

This is the rvalue version.

This functions is fmap on the functor in A of Result<A, E>.

Returns

The modified valid value if exists, or an error otherwise.

transform() [2/2]

template<typename T, typename E = std::error_code>

template<typename C>
requires std::invocable<C, const T&>

auto Acts::Result< T, E >::transform

(

C &&

callable

)

const &

Transforms the value contained in this result.

Applying a function f to a valid value x returns f(x), while applying f to an invalid value returns another invalid value.

Parameters

[in]

callable

The transformation function to apply.

Note

This is the lvalue version.

This functions is fmap on the functor in A of Result<A, E>.

Returns

The modified valid value if exists, or an error otherwise.

value() [1/2]

template<typename T, typename E = std::error_code>

T & Acts::Result< T, E >::value

(

)

&

Retrieves the valid value from the result object.

Note

This is the lvalue version, returns a reference to the value

Returns

The valid value as a reference

value() [2/2]

template<typename T, typename E = std::error_code>

const T & Acts::Result< T, E >::value

(

)

const &

Retrieves the valid value from the result object.

Note

This is the lvalue version, returns a reference to the value

Returns

The valid value as a reference

value_or()

template<typename T, typename E = std::error_code>

template<typename U>
requires (std::same_as<std::decay_t<U>, T>)

std::conditional_t< std::is_reference_v< U >, const T &, T > Acts::Result< T, E >::value_or

(

U &&

v

)

const &

Retrieves the valid value from the result object, or returns a default value if no valid value exists.

Parameters

[in]

v

The default value to use if no valid value exists.

Note

This is the lvalue version.

This function always returns by value.

Returns

Either the valid value, or the given substitute.